Empty metal cans intended for beverage use and the like typically become contaminated with foreign material such as paper and wood dust during shipping by pallet and as they are being processed in a factory. In the latter case, contact between the cans and the surfaces of articles, such as plastic chains, used to convey the cans cause them to pick up a slight net electrostatic charge, attracting fine particles to the can walls.
The dust particles contaminating these cans are characteristically extremely small, measuring less than 10 microns in diameter. Any electrostatic charges on the cans induce opposite charges on the particles to attract and hold them on the can walls. To remove particles adhering to the walls, these opposite charges must be neutralized. Neutralizing the charges is difficult, however, because the charges holding each dust particle to a can wall are shielded by the dust particle itself. Moreover, once the electrostatic forces have been momentarily abated, the freed dust particles must be removed immediately before they can re-attach themselves to the container.
In the prior art, the processing of empty metal cans in preparation for filling them with beverages and the like included spraying the cans with water. This cleaning technique, however, removes only about one-half of the dust particles inside the cans. Moreover, the high humidity generated by the water sprays favors the growth and spread of microorganisms, creating additional problems in the typical factory environment.